In an inkjet print device of this type, the carriage, in its movement in the main scan direction, temporarily halts at each end of its mobility range before going on in an opposite direction. Thus, there is an accelerate/decelerate area at each end of the mobility range and a constant-speed area there between.
In addition, as the print head ejects ink while the carriage is moving, the ink hits recording paper at a position somewhat ahead of where it was ejected with respect to the direction of the movement. Therefore, if ink is ejected when the carriage is at the same position in the forward and return directions, aiming at the same position on an image with respect to the main scan direction, the ink hits different positions. To avoid such off-target hitting, the ink eject position needs be corrected at least either in the forward movement or in the return movement to hit the same position on the image.
The magnitude of the discrepancy between the ink eject position and the ink hitting position varies with the moving speed of the carriage (hereinafter, “carriage speed”). The ink eject position can be corrected relatively easily in the constant-speed area, but difficult in the accelerate/decelerate areas. In conventional inkjet print devices, therefore, print areas are specified inside the constant-speed area so that the print device prints only inside the constant-speed area.
Problems arise with the specification of print areas only inside the constant-speed area in the conventional inkjet print device. Printing takes time because of the presence of the accelerate/decelerate areas extending from the ends of the constant-speed area. For the same reason, the device is bulky too.
Further, the inkjet print device senses the carriage position with a linear encoder. Commercially available encoder have a maximum resolution of 150 dpi, whilst the image printed on recording paper has a resolution of 600 to 1200 dpi. The encoder output cannot be used straightly as position information to control ink ejection in high resolution printing.